Both geologic and climatic events helped to make Australia's fauna unique.[5] Australia was once part of the southern supercontinent Gondwana,[6] which also included South America, Africa, India and Antarctica. Gondwana began to break up 140 million years ago (MYA); 50 MYA Australia separated from Antarctica and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene epoch 5.3 MYA. The establishment and evolution of the present-day fauna was apparently shaped by the unique climate and the geology of the continent. As Australia drifted, it was, to some extent, isolated from the effects of global climate change. The unique fauna that originated in Gondwana, such as the marsupials, survived and adapted in Australia.[7]
After the Miocene, fauna of Asian origin were able to establish themselves in Australia. The Wallace Line — the hypothetical line separating the zoogeographical regions of Asia and Australasia — marks the tectonic boundary between the Eurasian and Indo-Australian plates. This continental boundary prevented the formation of land bridges and resulted in a distinct zoological distribution, with limited overlap, of most Asian and Australian fauna, with the exception of birds. Following the emergence of the circumpolar current in the mid-Oligocene era (some 15 MYA), the Australian climate became increasingly arid, giving rise to a diverse group of arid-specialised organisms, just as the wet tropical and seasonally wet areas gave rise to their own uniquely adapted species.[citation needed]
Mammals
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Australia has a rich mammalian fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, currently however there is limited taxonomic research into Australia's mammals.[9][10] The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145–99 MYA,[11] and that marsupials and placental mammals date from the Eocene 56–34 MYA,[12] when modern mammals first appeared in the fossil record. Although terrestrial marsupials and placental mammals did coexist in Australia in the Eocene, only the marsupials have survived to the present. Non-volant placental mammals made their reappearance in Australia in the Miocene, when Australia moved closer to Indonesia, and rodents started to appear reliably in the Late Miocene fossil record. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution.[13] For example, the top predator in Australia, the thylacine,[8] bore a striking resemblance to canids.[14] Gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle;[15] and the numbat and anteaters are both digging insectivores.[16] For the most part, mammals are not a highly visible part of the faunal landscape, as most species are nocturnal and many arboreal.
Monotremes and marsupials
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Two of the five living species of monotreme occur in Australia: the platypus and the short-beaked echidna,[17] the other three being echidnas that only occur in New Guinea. Monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young.[17] The platypus — a venomous, egg-laying, duck-billed amphibious mammal — is considered to be one of the strangest creatures in the animal kingdom. When it was first presented by Joseph Banks to English naturalists it was thought to be a hoax.[17][18] The short-beaked echidna is covered in hairy spikes with a tubular snout in the place of a mouth, and a tongue that can move in and out of the snout at a rate of 100 times a minute to capture termites.[18][19]
Australia has the world's largest and most diverse range of marsupials.[22] Marsupials are characterised by the presence of a pouch in which they rear their young after birth.[22] The carnivorous marsupials — Dasyuromorphia — are represented by two surviving families: the Dasyuridae with 51 members, and the Myrmecobiidae with the numbat as its sole extant species.[23] The Tasmanian tiger was the largest Dasyuromorphia[24] and the last living specimen of the family Thylacinidae died in captivity in 1936.[8] The world's largest surviving carnivorous marsupial is the Tasmanian devil; it is the size of a small dog and can hunt, although it is mainly a scavenger.[24][25] It became extinct on the mainland some 600 years ago, and is now found only in Tasmania.[25] There are four species of quoll, or "native cat", all of which are threatened species.[21] The eastern quoll for example is believed to have been extinct on the mainland since the 1960s, though there are efforts to reintroduce it.[26][27] The remainder of the Dasyuridae are referred to as "marsupial mice";[28] most weigh less than 100 g.[29] There are two species of marsupial mole — order Notoryctemorphia — that inhabit the deserts of Western Australia. These rare, blind and earless carnivorous creatures spend most of their time underground; little is known about them.[30][31]
The bandicoots and bilbies — order Peramelemorphia — are marsupial omnivores.[32] There are seven extant species in Australia, most of which are endangered.[33][34] These small creatures share several characteristic physical features: a plump, arch-backed body with a long, delicately tapering snout, large upright ears, long, thin legs, and a thin tail.[33] The evolutionary origin of this group is unclear, because they share characteristics from both carnivorous and herbivorous marsupials.
Marsupials with two front teeth (diprotodont) on the lower jaw and syndactyly are classified in the order Diprotodontia, and further into the suborders Vombatiformes, Macropodiformes and Phalangerida. The Vombatiformes include the koala and the three species of wombat. One of Australia's best-known marsupials, the koala is an arboreal species that feeds on the leaves of various species of eucalyptus.[35] Wombats, on the other hand, live on the ground and feed on grasses, sedges and roots.[35] Wombats use their diprotodont teeth and powerful claws to dig extensive burrow systems; they are mainly crepuscular and nocturnal.[35]
The Phalangerida includes six families and 26 species of possum and three families with 53 species of macropod. The possums are a diverse group of arboreal marsupials and vary in size from the little pygmy possum, weighing just 7 g,[36] to the cat-sized common ringtail and brushtail possums.[37][38] The sugar and squirrel gliders are common species of gliding possum, found in the eucalypt forests of eastern Australia, while the feathertail glider is the smallest glider species.[39][40] The gliding possums have membranes called "patagia" that extend from the fifth finger of their forelimb back to the first toe of their hind foot. These membranes, when outstretched, allow them to glide between trees.
The macropods are divided into three families: the Hypsiprymnodontidae, with the musky rat-kangaroo as its only member;[41] the Potoroidae, with 11 species; and the Macropodidae, with 45 species.[42] Macropods are found in all Australian environments except alpine areas. The Potoroidae include the bettongs, potaroos and rat-kangaroos, small species that make nests and carry plant material with their tails.[43] The Macropodiae include kangaroos, wallabies and associated species; size varies widely within this family. Most macropods have large hind legs and long, narrow hind feet,[44] with a distinctive arrangement of four toes, and powerfully muscled tails, which they use to hop around.[45] The musky rat-kangaroo is the smallest macropod and the only species that is quadrupedal not bipedal,[46] while the male red kangaroo is the largest, reaching a height of about 2 m and weighing up to 85 kg.
